The present invention relates to a vehicle control system and more particularly to a driving force control system for causing a reduction in driving force in response to brake demand or intention.
Driver's power demand on an automotive vehicle is detected by depression of or force exerted on an accelerator pedal. Likewise, driver's brake demand is detected by depression of or force exerted on a brake pedal of a brake system, or the state of a manual parking brake. Among various types of hydraulic brake systems, there is known a brake system which uses as a brake booster Master Vac (a trade name). The Master Vac is installed between a brake pedal and a master cylinder and uses a pressure differential between the engine manifold vacuum and the atmospheric pressure to activate an output rod. Via an input rod, brake pedal effort is transmitted to the output rod, and the output rod utilizes the movement of the input rod and the force of a power piston subject to the above mentioned pressure differential to apply force to the master cylinder piston. In order to minimize the transmission of a change in engine manifold vacuum to a vacuum chamber on one side of a power cylinder, there is provided a check valve between the engine intake manifold and Master Vac thereby to keep the vacuum within the vacuum chamber. However, the vacuum within the Master Vac tends to disappear during driving with a so-called heel and toe driving technique. During the driving with heel and toe technique, the depression of the brake pedal is repeated with the accelerator pedal kept depressed. Under this driving condition, since there is no introdction of new vacuum from the engine intake manifold to the vacuum chamber on one side of the power piston and the introduction of atmospheric air into the atmospheric chamber on the other side of the power piston is repeated, the vacuum within the Master Vac tends to disappear gradually. As a result, the function as the brake booster will disappear. In this case, the driver has to depress the brake pedal with a greater brake effort than the normal case to provide the same braking effect.
An object of the present invention is to provide a driving force control system for an automotive vehicle which automatically controls driving force to meet brake demand or intention. Thus, for example, even if a brake booster ceases its operation, effective braking is provided with reasonable brake effort.